The present invention relates to a press device using a piezoelectric element, and an actuator used in the device.
Conventional press machines or systems generally use a die closing, wedge-type or toggle-type mechanism for die opening and closing, with the die-closing mechanism being driven and operated by a hydraulic cylinder or an air cylinder.
Further, specialty-parts assembling machines and assembling jigs also generally use a hydraulic cylinder or an air cylinder as the actuator to attach parts brought into the jig, as in the above case.
The above-mentioned conventional presses that are generally used have, in addition to the complexity of their die-closing mechanism, the problem that when using electric signals to control the presses, it is difficult to synchronize the operation of the mechanism of the main body of the press to the die-closing mechanism because the die-closing mechanism is operated by a hydraulic cylinder or an air cylinder.
Generally, press systems or mechanisms using piezoelectric elements had the following problems:
1. Because the die was a fixed-stripper type, warping occurred while shearing the material to be processed. Further, an actuator using a piezoelectric element only operates compressively and breaks down in tension making it impossible to drive the die set. PA1 2. Since the structure is such that an actuator using a layer-type piezoelectric element directly drives a punch, its dismantling and replacement when damaged or degraded consumed a great deal of time. PA1 3. Since the actuator using a layer-type piezoelectric element was mounted directly on a die, the actuator had to be installed on another die to process parts of a different shape. PA1 4. The actuators or dies using a piezoelectric element required a special device to mount and hold them. PA1 5. Because the conventional actuator using a piezoelectric element was not installed as an independent device, a replacement of the actuator and the movable piece required a great amount of time. PA1 6. Because the insulation between the case and the actuator used an air space, a hazardous electrical shock could have been caused by a short circuit to the case during operation. PA1 7. It was impossible to measure length of stroke of the movable piece. PA1 8. In assembling the layer-type piezoelectric element and the movable piece into the drive mechanism, a space was created between the movable piece and the movement-receiving end of the drive mechanism because of insufficient processing precision. As a result, the drive mechanism became incapable of performing the desired operation. PA1 9. Because the case for the piezoelectric element was made of a material having a larger thermal expansion coefficient than that of the piezoelectric element, the case expanded slightly in size during operation and caused malfunctions. PA1 10. The case for the piezoelectric element was deformed by a high-load output and became incapable of reproducing the stroke length setting at no load. PA1 11. The movable piece in the actuator, which used ferrous material, was compressed by the high loading and resulted in a reduction of the length of the stroke. PA1 12. Because some conventional configurations had the layer-type piezoelectric element arranged in series with the resilient element that applies a compressive force constantly to the piezoelectric element, the length of the piezoelectric actuator needed to be longer than that of the layer-type piezoelectric element, thus limiting the compactness of the piezoelectric actuator. PA1 1. A first actuator with a piezoelectric element that expands and contracts in an axial direction in response to an applied voltage; PA1 2. A piezoelectric actuator used as a drive source to drive the first punch with vibrations; PA1 3. A movable stopper in the press die that has the punch in it in order to hold down work material during the shearing process; and PA1 4. A second actuator with a piezoelectric element, which is in the press die and used to return the movable stopper to its initial position. PA1 1. A piezoelectric element which expands and contracts in the axial direction in response to an applied voltage; PA1 2. A movable piece (or work piece) to transmit a displacement of the piezoelectric element externally; PA1 3. A resilient element to return the movable piece to a predetermined position; and PA1 4. The piezoelectric element and the resilient element are connected in parallel, thereby pre-stressing the piezoelectric element with the compressive force generated by the resilient element. PA1 1. The piezoelectric element used in the actuator comprises many layers of piezoelectric ceramic sheets made of material such as barium titanate porcelain. As is well known, when excited with an electric field, a piezoelectric element distorts itself in response to the direction of the electric field. Structuring the distorting direction as a result of the piezoelectric effect to match the laminating direction of the piezoelectric ceramic sheets will provide a relatively large elongation displacement for the piezoelectric element as a whole. Therefore, if the piezoelectric element is incorporated in a press die or an assembly jig as an actuator and is operated by electric signals to carry out die opening and closing of a press die and/or closing of an assembly jig, a material or part loaded on the press die or the assembly jig can be clamped in a predetermined position in the press die of the assembly jig. Its operation response time is much faster than if a hydraulic or air cylinder is used, and the operation can be timed directly by electric signals. PA1 2. In a press which uses an actuator using a piezoelectric element for a punch drive source, a movable stopper made of a stiff material is disposed in a die (press die) to hold down a material to be processed in a shearing process, and a clamping actuator using a piezoelectric element is disposed in the die independently from the punch drive source to return the movable stopper to its initial position. In this configuration, the punch shears the material while the movable stopper holds it down, thus reducing deformation of the material, such as warping. Moreover, incorporating the actuator in the die makes the press device more compact, and allows the actuator as the punch drive source to perform all of the stroke operations of the punch, so that it is not necessary to drive the die set. PA1 3. In a press device, which uses an actuator with a piezoelectric element as a punch drive source, when the actuator needs a replacement because of damage or deterioration, the structure allows the replacement of said actuator without having to dismantle the die section. This configuration facilitates dismantling of the punch for grinding, because the actuator has a piezoelectric element and the punch in contacted for transmission, and because the resilient element is used to press and hold the punch on the actuator in the die. PA1 4. In a press device, which uses an actuator with a piezoelectric element as a punch drive source, the structure eliminates the need of removing the actuator at the press die interface, and facilitates shearing materials with different shapes, by disposing a frame to mount the actuator and incorporating the die in this frame. See FIG. 1 and 9. PA1 5. In a press device, which uses an actuator with a piezoelectric element as a punch drive source, the structure eliminates the need for a special mounting location for the device, and allows fabrication of the device at a lower cost. This is done by disposing self-standing legs at the bottom of the frame or the die. PA1 6. The displacement of a piezoelectric element is transmitted externally through a movable piece, rather than by coupling the piezoelectric element with an external device. A guide plate to guide this movable piece is removable on the mounting side of the case. Therefore, the actuator takes a single and independent form, and allows easy replacement without having to dismantle the mechanism with the piezoelectric element and the movable piece whenever the piezoelectric element is damaged or deteriorated or the movable piece is worn out and in need of replacement. PA1 7. In addition, because an insulating element, also functioning as an axial stopper to stop the movable piece, is interposed between the piezoelectric element and the case, the actuator's position can be determined accurately and safely, and prevents a short circuit with the case during an insulation breakdown, eliminating the danger of electric shock to the operator. PA1 8. Furthermore, a displacement transmitting part for measuring the stroke, which is on the movable piece and projecting externally from the opening on the case surface, measures the operation stroke directly and accurately on the actuator side. PA1 9. A position-adjusting mechanism on the case end is capable of variably adjusting a mounting position of the movable piece, both in coarse and fine adjustments, allows an operator to accurately adjust the extension amount of the movable piece. This allows the desired depth of operation after the piezoelectric element is adjusted within the case. PA1 10. The case is formed with two kinds of material, one having a lower thermal coefficient of expansion and the other having a higher thermal coefficient at expansion than that of the piezoelectric element in order to make the elongation of the piezoelectric element caused because of ambient temperature variations nearly equal to that of the case. Therefore, the structure eliminates variation in the extension amount of the movable piece from its initial setting caused by temperature variations, and drives the actuator from an initially set condition without adjustment, regardless of ambient temperature variation. PA1 11. Furthermore, using in part of the case a ceramic material that can withstand the high load needed to cause a deformation of the piece being processed, enables, together with the function described in Item (10) above, the reduction of the elongation of the case caused from the load present during operation of the piezoelectric element, and prevents the stroke from becoming smaller, thus realizing a more compact actuator and eliminating the need for rust prevention treatment on the case surface. PA1 12. Structuring the movable piece with highly longitudinally resilient material having a higher longitudinal resilience than steel, i.e. being "stiffer" than steel, such as cemented carbide or ceramic, reduces the compressive distortion of the movable piece caused from a load during operation of the piezoelectric element. This structure prevents the effective operating stroke from becoming smaller, making the actuator more compact, and eliminating the need for rust preventive treatment on slides, as well as reducing slide play. PA1 13. Connecting the piezoelectric element in parallel with a resilient element to apply a compressive stress constantly to the piezoelectric element makes the total length of the piezoelectric actuator shorter than the conventional actuator typically connected in series, thus making it possible for the actuator to be more compact.
The present invention was made in light of the above problems. Its first purpose is to provide an actuator using materials and parts that will allow simplified construction and that will make the actuator able to respond speedily to the operation and able to synchronize its motion directly from electric signals.
The second purpose of the present invention is to enhance processing precision and durability of a relatively low-cost press with replaceable parts that can be easily dismantled.
The third purpose of the present invention is to provide an actuator using a piezoelectric element which is easily handled and of high precision.
The fourth purpose of the present invention is to provide an actuator using a piezoelectric element which is compact, of high precision, and reliable.